Full color reflective display with multichromatic sub-pixels

ABSTRACT

A full color, reflective display having superior saturation and brightness is achieved with a novel display element comprising multichromatic elements. In one embodiment a capsule includes more than three species of particles which differ visually. One embodiment of the display employs three sub-pixels, each sub-pixel comprising a capsule including three species of particles which differ visually. Another embodiment of the display employs color filters to provide different visual states to the user. The display element presents a visual display in response to the application of an electrical signal to at least one of the capsules.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Ser. No. 60/081,362 filed Apr.10, 1998, the contents of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to electronic displays and, in particular,to full color electrophoretic displays and methods of creatingfull-color microencapsulated eletrophoretic displays.

BACKGROUND OF THE INVENTION

There are a number of enhanced reflective display media which offernumerous benefits such as enhanced optical appearance, the ability to beconstructed in large form factors, capable of being formed usingflexible substrates, characterized by easy manufacturability andmanufactured at low cost. Such reflective display media includemicroencapsulated electrophoretic displays, rotating ball displays,suspended particle displays, and composites of liquid crystals withpolymers (known by many names including but not limited to polymerdispersed liquid crystals, polymer stabilized liquid crystals, andliquid crystal gels). Electrophoretic display media, generallycharacterized by the movement of particles through an applied electricfield, are highly reflective, can be made bistable, and consume verylittle power. Further, encapsulated electrophoretic displays also may beprinted. These properties allow encapsulated electrophoretic displaymedia to be used in many applications for which traditional electronicdisplays are not suitable, such as flexible, printed displays.

While bichromatic electrophoretic displays have been demonstrated in alimited range of colors (e.g. black/white or yellow/red), to date therehas not been successful commercialization of a full-colorelectrophoretic display. Indeed, no reflective display technology todate has shown itself capable of satisfactory color. Full-colorreflective displays typically are deficient when compared to emissivedisplays in at least two important areas: brightness and colorsaturation.

One traditional technique for achieving a bright, full-color displaywhich is known in the art of emissive displays is to create sub-pixelsthat are red, green and blue. In this system, each pixel has two states:on, or the emission of color; and off. Since light blends from thesesub-pixels, the overall pixel can take on a variety of colors and colorcombinations. In an emissive display, the visual result is the summationof the wavelengths emitted by the sub-pixels at selected intensities,white is seen when red, green and blue are all active in balancedproportion or full intensity. The brightness of the white image iscontrolled by the intensities of emission of light by the sub-pixels.Black is seen when none are active or, equivalently, when all areemitting at zero intensity. As an additional example, a red visualdisplay appears when the red sub-pixel is active while the green andblue are inactive, and thus only red light is emitted.

It is known that this method can be applied to bichromatic reflectivedisplays, typically using the cyan-magenta-yellow subtractive colorsystem. In this system, the reflective sub-pixels absorb characteristicportions of the optical spectrum, rather than generating characteristicportions of the spectrum as do the pixels in an emissive display. Whitereflects everything, or equivalently absorbs nothing. A coloredreflective material reflects light corresponding in wavelength to thecolor seen, and absorbs the remainder of the wavelengths in the visiblespectrum. To achieve a black display, all three sub-pixels are turnedon, and they absorb complementary portions of the spectrum.

However, the colors displayed by a full-color display as described aboveare sub-optimal. For example, to display red, one pixel displaysmagenta, one displays yellow, and one displays white. The whitesub-pixel reduces the saturation of red in the image and reduces displaycontrast. The overall effect is a washed out red. This furtherillustrates why no method to date has been capable of generating ahigh-contrast, high-brightness full color reflective display with goodcolor saturation.

SUMMARY OF THE INVENTION

This invention teaches practical ways to achieve brighter, moresaturated, reflective full-color displays than previously known,particularly full-color encapsulated, electrophoretic displays.

An object of the invention is to provide a brighter, more satured,reflective full-color display. In some embodiments, the displays arehighly flexible, can be manufactured easily, consume little power, andcan, therefore, be incorporated into a variety of applications. Theinvention features a printable display comprising an encapsulatedelectrophoretic display medium. In an embodiment the display media canbe printed and, therefore the display itself can be made inexpensively.

An encapsulated electrophoretic display can be constructed so that theoptical state of the display is stable for some length of time. When thedisplay has two states which are stable in this manner, the display issaid to be bistable. If more than two states of the display are stable,then the display can be said to be multistable. For the purpose of thisinvention, the terms bistable and multistable, or generally, stable,will be used to indicate a display in which any optical state remainsfixed once the addressing voltage is removed. The definition of a stablestate depends on the application for the display. A slowly-decayingoptical state can be effectively stable if the optical state issubstantially unchanged over the required viewing time. For example, ina display which is updated every few minutes, a display image which isstable for hours or days is effectively bistable or multistable, as thecase may be, for that application. In this invention, the terms bistableand multistable also indicate a display with an optical statesufficiently long-lived as to be effectively stable for the applicationin mind. Alternatively, it is possible to construct encapsulatedelectrophoretic displays in which the image decays quickly once theaddressing voltage to the display is removed (i.e., the display is notbistable or multistable). As will be described, in some applications itis advantageous to use an encapsulated electrophoretic display which isnot bistable or multistable. Whether or not an encapsulatedelectrophoretic display is stable, and its degree of stability, can becontrolled through appropriate chemical modification of theelectrophoretic particles, the suspending fluid, the capsule, and bindermaterials.

An encapsulated electrophoretic display may take many forms. The displaymay comprise capsules dispersed in a binder. The capsules may be of anysize or shape. The capsules may, for example, be spherical and may havediameters in the millimeter range or the micron range, but is preferablyfrom ten to a few hundred microns. The capsules may be formed by anencapsulation technique, as described below. Particles may beencapsulated in the capsules. The particles may be two or more differenttypes of particles. The particles may be colored, luminescent,light-absorbing or transparent, for example. The particles may includeneat pigments, dyed (laked) pigments or pigment/polymer composites, forexample. The display may further comprise a suspending fluid in whichthe particles are dispersed.

The successful construction of an encapsulated electrophoretic displayrequires the proper interaction of several different types of materialsand processes, such as a polymeric binder and, optionally, a capsulemembrane. These materials must be chemically compatible with theelectrophoretic particles and fluid, as well as with each other. Thecapsule materials may engage in useful surface interactions with theelectrophoretic particles, or may act as a chemical or physical boundarybetween the fluid and the binder. Various materials and combinations ofmaterials useful in constructing encapsulated electrophoretic displaysare described in co-pending application Ser. No. 09/140,861, thecontents of which are incorporated by reference herein.

In some cases, the encapsulation step of the process is not necessary,and the electrophoretic fluid may be directly dispersed or emulsifiedinto the binder (or a precursor to the binder materials) and aneffective “polymer-dispersed electrophoretic display” constructed. Insuch displays, voids created in the binder may be referred to ascapsules or microcapsules even though no capsule membrane is present.The binder dispersed electrophoretic display may be of the emulsion orphase separation type.

Throughout the specification, reference will be made to printing orprinted. As used throughout the specification, printing is intended toinclude all forms of printing and coating, including: premeteredcoatings such as patch die coating, slot or extrusion coating, slide orcascade coating, and curtain coating; roll coating such as knife overroll coating, forward and reverse roll coating; gravure coating; dipcoating; spray coating; meniscus coating; spin coating; brush coating;air knife coating; silk screen printing processes; electrostaticprinting processes; thermal printing processes; and other similartechniques. A “printed element” refers to an element formed using anyone of the above techniques.

As noted above, electrophoretic display elements can be encapsulated.Throughout the Specification, reference will be made to “capsules,”“pixels,” and “sub-pixels.” A pixel display element can be formed by oneor more capsules or sub-pixels. A sub-pixel may itself comprise one ormore capsules or other structures.

A full color, reflective display having superior saturation andbrightness is achieved with a novel display element comprisingmultichromatic sub-elements. One embodiment of the display employs threesub-pixels, each sub-pixel comprising a capsule including three speciesof particles which differ visually. Another embodiment of the displayemploys color filters combined with an encapsulated electrophoreticdisplay to provide different visual states. In still another embodiment,the display employs display elements capable of more than three visualstates. In yet another embodiment, the visual display states areselected from specific colors, for example, the primary colors red,green and blue, or their complements, and white and/or black. Thedisplay element presents a visual display in response to the applicationof an electrical signal to at least one of the capsules.

In one aspect, the present invention relates to an electrophoreticdisplay element. The display element comprises a first capsule includinga first species of particles having a first optical property and asecond species of particles having a second optical property visuallydifferent from the first optical property. The display element furthercomprises a second capsule including a third species of particles havinga third optical property and a fourth species of particles having afourth optical property visually different from the third opticalproperty. The display element presents a visual display in response tothe application of an electrical signal to at least one of the first andsecond capsules. The first optical property and the third opticalproperty can be, but are not required to be, substantially similar inappearance.

The electrophoretic display element can further comprise a fifth speciesof particles having a fifth optical property visually different from thefirst and second optical properties in the first capsule. It can alsocomprise a sixth species of particles having a sixth optical propertyvisually different from the third and fourth optical properties in thesecond capsule. It can also include a third capsule having a seventhspecies of particles having a seventh optical property, an eighthspecies of particles having a eighth optical property, and a ninthspecies of particles having a ninth optical property.

The electrophoretic display element can include particles such that thefirst, third and seventh optical properties have a white visualappearance. The electrophoretic display element can include particlessuch that the second, fourth and eighth optical properties have a blackvisual appearance. The electrophoretic display element can have at leastone of the optical properties be red, green, blue, yellow, cyan, ormagenta in visual appearance. The electrophoretic display element canhave at least one of the optical properties comprising color,brightness, or reflectivity.

The electrophoretic display element can have capsules which include asuspending fluid. The suspending fluid can be substantially clear, or itcan be dyed or otherwise colored.

In another aspect, the present invention relates to a display apparatuscomprising at least one display element which includes at least twocapsules such as are described above and at least one electrode adjacentto the display element, wherein the apparatus presents a visual displayin response to the application of an electrical signal via the electrodeto the display element.

The display apparatus can include a plurality of electrodes adjacent thedisplay element. The plurality of electrodes can include at least onewhich has a size different from others of the plurality of electrodes,and can include at least one which has a color different from others ofthe plurality of electrodes.

In another aspect, the present invention relates to an electrophoreticdisplay element comprising a capsule containing a first species ofparticles having a first optical property, a second species of particleshaving a second optical property visually different from the firstoptical property, a third species of particles having a third opticalproperty visually different from the first and second optical propertiesand a fourth species of particles having a fourth optical propertyvisually different from the first, second, and third optical propertiessuch that the element presents a visual display in response to theapplication of an electrical signal to the capsule. The electrophoreticdisplay element can also include a suspending fluid within the capsule.

In yet another aspect, the present invention relates to anelectrophoretic display element comprising a capsule containing a firstspecies of particles having a first optical property, a second speciesof particles having a second optical property visually different fromthe first optical property, a third species of particles having a thirdoptical property visually different from the first and second opticalproperties, a fourth species of particles having a fourth opticalproperty visually different from the first, second, and third opticalproperties, and a fifth species of particles having a fifth opticalproperty visually different from the first, second, third, and fourthoptical properties such that the element presents a visual display inresponse to the application of an electrical signal to said capsule. Theelectrophoretic display element can also include a suspending fluidwithin the capsule.

In still another aspect, the present invention relates to a method ofmanufacturing an electrophoretic display. The manufacturing methodcomprises the steps of providing a first capsule containing a firstspecies of particles having a first optical property and a secondspecies of particles having a second optical property visually differentfrom the first optical property, and providing a second capsulecontaining a third species of particles having a third optical propertyand a fourth species of particles having a fourth optical propertyvisually different from the third optical property, such that when anelectrical signal is applied to at least one of the first and secondcapsules the element presents a visual display in response to thesignal. In this method of manufacture, the first optical property andthe third optical property can be substantially similar in appearance.

In still a further aspect, the present invention relates to a method ofmanufacturing an electrophoretic display. This manufacturing methodcomprises the steps of providing a first capsule containing a firstspecies of particles having a first optical property, a second speciesof particles having a second optical property visually different fromthe first optical property and containing a third species of particleshaving a third optical property visually different from the first andsecond optical properties, providing a second capsule containing afourth species of particles having a fourth optical property, a fifthspecies of particles having a fifth optical property visually differentfrom the fourth optical property and a sixth species of particles havinga sixth optical property visually different from the fourth and fifthoptical properties, and providing a third capsule containing a seventhspecies of particles having a seventh optical property, an eighthspecies of particles having a eighth optical property visually differentfrom the seventh optical property, and a ninth species of particleshaving a ninth optical property visually different from the seventh andeighth optical properties, such that when an electrical signal isapplied to at least one of the first, second and third capsules, theelement presents a visual display in response to the signal.

The manufacturing method can include the step of providing a firstcapsule wherein the third optical property is red visual appearance, oris yellow visual appearance. The manufacturing method can include thestep of providing a second capsule wherein the sixth optical property isgreen visual appearance, or is cyan visual appearance. The manufacturingmethod can include the step of providing a third capsule wherein theninth optical property is blue visual appearance, or is magenta visualappearance. The manufacturing method can include the step of providingcapsules wherein the first, fourth and seventh optical properties arewhite visual appearance, or wherein the second, fifth and eighth opticalproperties are black visual appearance.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is pointed out with particularity in the appended claims.The advantages of the invention described above, together with furtheradvantages, may be better understood by referring to the followingdescription taken in conjunction with the accompanying drawings. In thedrawings, like reference characters generally refer to the same partsthroughout the different views. Also, the drawings are not necessarilyto scale, emphasis instead generally being placed upon illustrating theprinciples of the invention.

FIG. 1A is a diagrammatic side view of an embodiment of arear-addressing electrode structure for a particle-based display inwhich a smaller electrode has been placed at a voltage relative to thelarge electrode causing the particles to migrate to the smallerelectrode.

FIG. 1B is a diagrammatic side view of an embodiment of arear-addressing electrode structure for a particle-based display inwhich the larger electrode has been placed at a voltage relative to thesmaller electrode causing the particles to migrate to the largerelectrode.

FIG. 1C is a diagrammatic top-down view of one embodiment of arear-addressing electrode structure.

FIG. 1D is a diagrammatic perspective view of one embodiment of adisplay element having three sub-pixels, each sub-pixel comprising arelatively larger rear electrode and a relatively smaller rearelectrode.

FIG. 2A is a diagrammatic side view of an embodiment of arear-addressing electrode structure having a retroreflective layerassociated with the larger electrode in which the smaller electrode hasbeen placed at a voltage relative to the large electrode causing theparticles to migrate to the smaller electrode.

FIG. 2B is a diagrammatic side view of an embodiment of arear-addressing electrode structure having a retroreflective layerassociated with the larger electrode in which the larger electrode hasbeen placed at a voltage relative to the smaller electrode causing theparticles to migrate to the larger electrode.

FIG. 2C is a diagrammatic side view of an embodiment of arear-addressing electrode structure having a retroreflective layerdisposed below the larger electrode in which the smaller electrode hasbeen placed at a voltage relative to the large electrode causing theparticles to migrate to the smaller electrode.

FIG. 2D is a diagrammatic side view of an embodiment of arear-addressing electrode structure having a retroreflective layerdisposed below the larger electrode in which the larger electrode hasbeen placed at a voltage relative to the smaller electrode causing theparticles to migrate to the larger electrode.

FIG. 3A is a diagrammatic side view of an embodiment of an addressingstructure in which a direct-current electric field has been applied tothe capsule causing the particles to migrate to the smaller electrode.

FIG. 3B is a diagrammatic side view of an embodiment of an addressingstructure in which an alternating-current electric field has beenapplied to the capsule causing the particles to disperse into thecapsule, obscuring a rear substrate.

FIG. 3C is a diagrammatic side view of an embodiment of an addressingstructure having transparent electrodes, in which a direct-currentelectric field has been applied to the capsule causing the particles tomigrate to the smaller electrode, revealing a rear substrate.

FIG. 3D is a diagrammatic side view of an embodiment of an addressingstructure having transparent electrodes, in which an alternating-currentelectric field has been applied to the capsule causing the particles todisperse into the capsule.

FIG. 3E is a diagrammatic side view of an embodiment of an addressingstructure for a display element having three sub-pixels.

FIG. 3F is a diagrammatic side view of an embodiment of a dual particlecurtain mode addressing structure addressing a display element to appearwhite.

FIG. 3G is a diagrammatic side view of an embodiment of a dual particlecurtain mode addressing structure addressing a display element to appearred.

FIG. 3H is a diagrammatic side view of an embodiment of a dual particlecurtain mode addressing structure addressing a display element to absorbred light.

FIG. 3I is a diagrammatic side view of an embodiment of a dual particlecurtain mode addressing structure for a display element having threesub-pixels, in which the display is addressed to appear red.

FIG. 3J is a diagrammatic side view of another embodiment of a dualparticle curtain mode addressing structure for a display element.

FIG. 3K is a diagrammatic plan view of an embodiment of aninterdigitated electrode structure.

FIG. 3L is a diagrammatic side view of another embodiment of a dualparticle curtain mode display structure having a dyed fluid and twospecies of particles, addressed to absorb red.

FIG. 3M is a diagrammatic side view of another embodiment of a dualparticle curtain mode display structure having clear fluid and threespecies of particles, addressed to absorb red.

FIG. 4A is a diagrammatic side view of an embodiment of arear-addressing electrode structure for a particle-based display havingcolored electrodes and a white electrode, in which the coloredelectrodes have been placed at a voltage relative to the white electrodecausing the particles to migrate to the colored electrodes.

FIG. 4B is a diagrammatic side view of an embodiment of arear-addressing electrode structure for a particle-based display havingcolored electrodes and a white electrode, in which the white electrodehas been placed at a voltage relative to the colored electrodes causingthe particles to migrate to the white electrode.

FIG. 5 is a diagrammatic side view of an embodiment of a color displayelement having red, green, and blue particles of differentelectrophoretic mobilities.

FIGS. 6A–6B depict the steps taken to address the display of FIG. 5 todisplay red.

FIGS. 7A–7D depict the steps taken to address the display of FIG. 5 todisplay blue.

FIGS. 8A–8C depict the steps taken to address the display of FIG. 5 todisplay green.

FIG. 9 is a cross-sectional view of a rear electrode addressingstructure that is formed by printing.

FIG. 10 is a perspective view of an embodiment of a control gridaddressing structure.

DETAILED DESCRIPTION OF THE INVENTION

An electronic ink is an optoelectronically active material thatcomprises at least two phases: an electrophoretic contrast media phaseand a coating/binding phase. The electrophoretic phase comprises, insome embodiments, a single species of electrophoretic particlesdispersed in a clear or dyed medium, or more than one species ofelectrophoretic particles having distinct physical and electricalcharacteristics dispersed in a clear or dyed medium. In some embodimentsthe electrophoretic phase is encapsulated, that is, there is a capsulewall phase between the two phases. The coating/binding phase includes,in one embodiment, a polymer matrix that surrounds the electrophoreticphase. In this embodiment, the polymer in the polymeric binder iscapable of being dried, crosslinked, or otherwise cured as intraditional inks, and therefore a printing process can be used todeposit the electronic ink onto a substrate.

In one embodiment, the ink may comprise sub-pixels capable of displayingdifferent colors. Sub-pixels may be grouped to form pixels. In oneparticular embodiment, each sub-pixel contains red particles, greenparticles, and blue particles, respectively. In another particularembodiment, each sub-pixel contains cyan particles, yellow particles,and magenta particles, respectively. In each example, each sub-pixel canadditionally include particles which are white and particles which areblack. By addressing each sub-pixel to display some fraction of itscolored particles, and some portion of the white and black particles, apixel can be caused to give an appearance corresponding to a selectedcolor at a selected brightness level.

An electronic ink is capable of being printed by several differentprocesses, depending on the mechanical properties of the specific inkemployed. For example, the fragility or viscosity of a particular inkmay result in a different process selection. A very viscous ink wouldnot be well-suited to deposition by an inkjet printing process, while afragile ink might not be used in a knife over roll coating process.

The optical quality of an electronic ink is quite distinct from otherelectronic display materials. The most notable difference is that theelectronic ink provides a high degree of both reflectance and contrastbecause it is pigment based (as are ordinary printing inks). The lightscattered from the electronic ink comes from a very thin layer ofpigment close to the top of the viewing surface. In this respect itresembles an ordinary, printed image. Also, electronic ink is easilyviewed from a wide range of viewing angles in the same manner as aprinted page, and such ink approximates a Lambertian contrast curve moreclosely than any other electronic display material. Since electronic inkcan be printed, it can be included on the same surface with any otherprinted material, including traditional inks. Electronic ink can be madeoptically stable in all display configurations, that is, the ink can beset to a persistent optical state. Fabrication of a display by printingan electronic ink is particularly useful in low power applicationsbecause of this stability.

Electronic ink displays are novel in that they can be addressed by DCvoltages and draw very little current. As such, the conductive leads andelectrodes used to deliver the voltage to electronic ink displays can beof relatively high resistivity. The ability to use resistive conductorssubstantially widens the number and type of materials that can be usedas conductors in electronic ink displays. In particular, the use ofcostly vacuum-sputtered indium tin oxide (ITO) conductors, a standardmaterial in liquid crystal devices, is not required. Aside from costsavings, the replacement of ITO with other materials can providebenefits in appearance, processing capabilities (printed conductors),flexibility, and durability. Additionally, the printed electrodes are incontact only with a solid binder, not with a fluid layer (like liquidcrystals). This means that some conductive materials, which wouldotherwise dissolve or be degraded by contact with liquid crystals, canbe used in an electronic ink application. These include opaque metallicinks for the rear electrode (e.g., silver and graphite inks), as well asconductive transparent inks for either substrate. These conductivecoatings include semiconducting colloids, examples of which are indiumtin oxide and antimony-doped tin oxide. Organic conductors (polymericconductors and molecular organic conductors) also may be used. Polymersinclude, but are not limited to, polyaniline and derivatives,polythiophene and derivatives, poly3,4-ethylenedioxythiophene (PEDOT)and derivatives, polypyrrole and derivatives, and polyphenylenevinylene(PPV) and derivatives. Organic molecular conductors include, but are notlimited to, derivatives of naphthalene, phthalocyanine, and pentacene.Polymer layers can be made thinner and more transparent than withtraditional displays because conductivity requirements are not asstringent.

As an example, there are a class of materials called electroconductivepowders which are also useful as coatable transparent conductors inelectronic ink displays. One example is Zelec ECP electroconductivepowders from DuPont Chemical Co. of Wilmington, Del.

It is possible to produce any selected color from the superposition ofsuitable proportions of three properly chosen colors. In one embodiment,the colors red, green, and blue can be combined in various proportionsto produce an image which is perceived as a selected color. Emissive ortransmissive displays operate according to additive rules, where theperceived color is created by summing the emission wavelengths of aplurality of emitting or transmitting objects. For an emissive ortransmissive display which includes three sub-pixels, one of which canproduce red light, one green light, and one blue light, respectively,one can generate all colors, as well as white and black. At one extreme,the combination of all three at full intensity is perceived as white,and at the other, the combination of all three at zero intensity isperceived as black. Specific combinations of controlled proportions ofthese three colors can be used to represent other colors.

In a reflective display, the light which a viewer perceives is theportion of the spectrum which is not absorbed when the light to bereflected falls on the reflector surface. One may thus consider areflecting system as a subtractive system, that is, that each reflectivesurface “subtracts” from the light that portion which the reflectorabsorbs. The color of a reflector represents the wavelengths of lightthe reflector absorbs. A yellow reflector absorbs substantially bluelight. A magenta reflector absorbs substantially green light. A cyanreflector absorbs substantially red light. Thus, in an alternativeembodiment employing reflectors, nearly the same results as an emissivesystem can be obtained by use of the three colors cyan, yellow, andmagenta as the primary colors, from which all other colors, includingblack but not white, can be derived. To obtain white from such adisplay, one must further introduce a third state per sub-pixel, namelywhite.

One approach which may be taken to overcome the shortcomings inherent intwo state displays is to create a display comprising individual pixelsor pixels comprising sub-pixels that can support multiple color states.The use of multiple color states permits more robust color rendition andprovides better contrast than is possible with two color states perpixel or per sub-pixel. For example, using a microencapsulatedelectrophoretic display, a single microcapsule with five kinds ofparticles could display white, cyan, magenta, yellow, or black all withexcellent saturation. By foregoing black and using cyan/magenta/yellowto combine to black, a similar effect can be achieved with a displayelement capable of four color states.

The invention can also utilize any reflective display element that cancreate three color states within a single sub-pixel, where sub-pixelsare combined to generate a variety of overall pixel colors. Such adisplay is capable of greatly improved appearance yet relies on onlythree color states per sub-pixel instead of four or five or more. Asub-pixel having only three color states can have advantages with regardto the operation of the display. Fewer and simpler applied voltagesignals are needed to operate each sub-pixel of the display element, Asub-pixel having fewer stable states may be capable of being addressedmore quickly than one with more stable states.

Various methods are possible by which three color states could beachieved within a single addressable region, which can be a displayelement sub-pixel. For example, a microencapsulated electrophoreticdisplay element sub-pixel may contain particles in a clear suspensionmedium. A simple addressing method is to provide white particles havinga positive charge, cyan particles having a negative charge, and redparticles having no charge. In this example, white is achieved when thetop electrode is negative and the bottom electrodes are both positive.Cyan is achieved when the top electrode is positive and the bottomelectrodes are both negative. Red is achieved when the top electrode isset to ground, one bottom electrode is positive and attracts the cyanparticles, and the other bottom electrode is negative and attracts thewhite particles, so that the red particles are uppermost and are seen.

Another example combines top and bottom motion with a sideways orso-called in-plane switching, control grid or shutter-effect method. Inone example, red particles have strong positive charge, black particleshave lesser positive charge, and the sub-pixel of the displayincorporates a white sheet behind a clear bottom electrode. The clearbottom electrode comprises a larger sub-electrode and a smallersub-electrode. In this example, using a shutter effect, red is achievedwhen the top electrode has a negative voltage and the bottom electrode,including both subelectrodes, has a positive voltage. Black is achievedwhen the top electrode has a positive voltage and the bottom electrode,including both subelectrodes, has a negative voltage. White is achievedwhen the smaller subelectrode of the bottom electrode is switched to anegative voltage but the top electrode and the larger subelectrode ofthe bottom electrode is switched to a less negative voltage. Thus thered and black particles are attracted to cluster at the smallersub-electrode, with the slower black particles clustering on top andblocking from sight the red particles, and the bulk of the microcapsuleis clear, allowing the white sheet to be visible. The top electrode maybe masked so that the clustered particles are not visible. Additionally,the backing sheet could be replaced with a backlight or color filter andbacklight. In another embodiment, a brief alternating voltage signal maybe used prior to addressing methods described above to mix the particlesinto a random order.

While the methods described discuss particles, any combination of dyes,liquids droplets and transparent regions that respond to electrophoreticeffects could also be used. Particles of various optical effects may becombined in any suitable proportion. For example, certain colors may beover- or under-populated in the electrophoretic suspension to accountfor the sensitivities of the human eye and to thereby achieve a morepleasing or uniform effect. Similarly, the sizes of the sub-pixels mayalso be disproportionate to achieve various optical effects.

Although these examples describe microencapsulated electrophoreticdisplays, the invention can be utilized across other reflective displaysincluding liquid crystal, polymer-dispersed liquid crystal, rotatingball, suspended particle and any other reflective display capable ofimaging three colors. For example, a bichromal rotating ball (orpyramid, cube, etc.) could be split into regions of multiple colors. Oneway to address such a display element would be to provide differingcharge characteristics (such as charged vertices in the case of thepyramid) and to use various combinations and sequences of electrodevoltage potentials across the surrounding top, bottom, or sideelectrodes to rotate the shape in a desired manner. In short, manyaddressing schemes are possible by which a sub-pixel in a direct colorreflective display could be switched among three colors. Such switchingmechanism will vary by the nature of the display and any suitable meansmay be used.

One embodiment of the invention is to separate each pixel into threesub-pixels, each sub-pixel being capable of displaying three colorstates, and to choose as the color state combinations a first sub-pixelbeing capable of displaying white, cyan or red, a second sub-pixel beingcapable of displaying white, magenta or green, and a third sub-pixelbeing capable of displaying white, yellow or blue. As has already beenexplained, for a reflective display, black can be displayed with thethree sub-pixels turned to red, green and blue, respectively. Thisdisplay achieves a more saturated black than is achieved under thetwo-state system. Alternatively, red is displayed with the sub-pixelsturned to red, magenta and yellow, respectively, which offers a moresaturated red than is obtained with a two-state system. Other colors maybe obtained by suitable choices of the individual states of thesub-pixels.

Another embodiment of the invention is to separate each pixel into threesub-pixels, each sub-pixel being capable of displaying three colorstates, and to choose as the color state combinations a first sub-pixelbeing capable of displaying white, cyan or black, a second sub-pixelbeing capable of displaying white, magenta or black, and a thirdsub-pixel being capable of displaying white, yellow or black. In thisembodiment, black and white are displayed directly with high saturation.For example, to display red, the first (cyan) sub-pixel is set to eitherwhite or black to achieve a dimmer or brighter color, respectively, thesecond sub-pixel is set to magenta, and the last sub-pixel is set toyellow.

Another embodiment of the invention is to separate each pixel into threesub-pixels, each sub-pixel being capable of displaying three colorstates, and to choose as the color state combinations a first sub-pixelbeing capable of displaying white, red or black, a second sub-pixelbeing capable of displaying white, green or black, and a third sub-pixelbeing capable of displaying white, blue or black. In this embodiment,black and white are displayed directly with high saturation. Forexample, to display red, the first sub-pixel is set to red, and thesecond and the third sub-pixels are set to either white or black toachieve a dimmer or brighter color, respectively.

While the embodiments above describe a pixel of three sub-pixels, eachsub-pixel having three possible color states, the invention is embodiedby any pixel containing two or more sub-pixels, where at least onesub-pixel can achieve three or more colors. In this manner a bettereffect can be achieved for reflective displays than can be achieved byadopting the simple two-state sub-pixel color change technique that iscommon to emissive displays.

Additionally, the invention can be extended to four or more color statesto permit full color displays without the need for sub-pixels, andillustrates addressing mechanisms that work for three states and whichcan be extended or combined to achieve a display with four or morestates.

Another means of generating color in a microencapsulated display mediumis the use of color filters in conjunction with a contrast-generatingoptical element. One manifestation of this technique is to use a pixelelement which switches between white and black. This, in conjunctionwith the color filter, allows for switching between a light and darkcolored state to occur. However, it is known to those skilled in the artthat different numbers of color filters (ranging from one to three) canbe used in a sub-pixel, depending on how many colors are desired. Also,the microencapsulated particle display can switch between colors otherthan white and black. In this case, it is advantageous to use a colorfilter which is opposed (in a color sense) to the color of the pixel.For example, a yellow color filter used with a blue or whiteelectrophoretic display would result in a green or yellow color to thatelement.

Additionally, there is an electrophoretic device known as a “shuttermode” display, in which particles are switched electrically between awidely-dispersed state on one electrode and a narrow band on the otherelectrode. Such a device can act as a transmissive light valve orreflective display. Color filters can be used with such a device.

Referring now to FIGS. 1A and 1B, an addressing scheme for controllingparticle-based displays is shown in which electrodes are disposed ononly one side of a display, allowing the display to be rear-addressed.Utilizing only one side of the display for electrodes simplifiesfabrication of displays. For example, if the electrodes are disposed ononly the rear side of a display, both of the electrodes can befabricated using opaque materials, which may be colored, because theelectrodes do not need to be transparent.

FIG. 1A depicts a single capsule 20 of an encapsulated display media. Inbrief overview, the embodiment depicted in FIG. 1A includes a capsule 20containing at least one particle 50 dispersed in a suspending fluid 25.The capsule 20 is addressed by a first electrode 30 and a secondelectrode 40. The first electrode 30 is smaller than the secondelectrode 40. The first electrode 30 and the second electrode 40 may beset to voltage potentials which affect the position of the particles 50in the capsule 20.

The particles 50 represent 0.1% to 20% of the volume enclosed by thecapsule 20. In some embodiments the particles 50 represent 2.5% to 17.5%of the volume enclosed by capsule 20. In preferred embodiments, theparticles 50 represent 5% to 15% of the volume enclosed by the capsule20. In more preferred embodiments the particles 50 represent 9% to 11%of the volume defined by the capsule 20. In general, the volumepercentage of the capsule 20 that the particles 50 represent should beselected so that the particles 50 expose most of the second, largerelectrode 40 when positioned over the first, smaller electrode 30. Asdescribed in detail below, the particles 50 may be colored any one of anumber of colors. The particles 50 may be either positively charged ornegatively charged.

The particles 50 are dispersed in a dispersing fluid 25. The dispersingfluid 25 should have a low dielectric constant. The fluid 25 may beclear, or substantially clear, so that the fluid 25 does not inhibitviewing the particles 50 and the electrodes 30, 40 from position 10. Inother embodiments, the fluid 25 is dyed. In some embodiments thedispersing fluid 25 has a specific gravity matched to the density of theparticles 50. These embodiments can provide a bistable display media,because the particles 50 do not tend to move in certain compositionsabsent an electric field applied via the electrodes 30, 40.

The electrodes 30, 40 should be sized and positioned appropriately sothat together they address the entire capsule 20. There may be exactlyone pair of electrodes 30, 40 per capsule 20, multiple pairs ofelectrodes 30, 40 per capsule 20, or a single pair of electrodes 30, 40may span multiple capsules 20. In the embodiment shown in FIGS. 1A and1B, the capsule 20 has a flattened, rectangular shape. In theseembodiments, the electrodes 30, 40 should address most, or all, of theflattened surface area adjacent the electrodes 30, 40. The smallerelectrode 30 is at most one-half the size of the larger electrode 40. Inpreferred embodiments the smaller electrode is one-quarter the size ofthe larger electrode 40; in more preferred embodiments the smallerelectrode 30 is one-eighth the size of the larger electrode 40. In evenmore preferred embodiments, the smaller electrode 30 is one-sixteenththe size of the larger electrode 40. It should be noted that referenceto “smaller” in connection with the electrode 30 means that theelectrode 30 addresses a smaller amount of the surface area of thecapsule 20, not necessarily that the electrode 30 is physically smallerthan the larger electrode 40. For example, multiple capsules 20 may bepositioned such that less of each capsule 20 is addressed by the“smaller” electrode 30, even though both electrodes 30, 40 are equal insize. It should also be noted that, as shown in FIG. 1C, electrode 30may address only a small corner of a rectangular capsule 20 (shown inphantom view in FIG. 1C), requiring the larger electrode 40 to surroundthe smaller electrode 30 on two sides in order to properly address thecapsule 20. Selection of the percentage volume of the particles 50 andthe electrodes 30, 40 in this manner allow the encapsulated displaymedia to be addressed as described below.

Electrodes may be fabricated from any material capable of conductingelectricity so that electrode 30, 40 may apply an electric field to thecapsule 20. As noted above, the rear-addressed embodiments depicted inFIGS. 1A and 1B allow the electrodes 30, 40 to be fabricated from opaquematerials such as solder paste, copper, copper-clad polyimide, graphiteinks, silver inks and other metal-containing conductive inks.Alternatively, electrodes may be fabricated using transparent materialssuch as indium tin oxide and conductive polymers such as polyaniline orpolythiopenes. Electrodes 30, 40 may be provided with contrastingoptical properties. In some embodiments, one of the electrodes has anoptical property complementary to optical properties of the particles50. Alternatively, since the electrodes need not be transparent, anelectrode can be constructed so as to display a selected color.

In one embodiment, the capsule 20 contains positively charged blackparticles 50, and a substantially clear suspending fluid 25. The first,smaller electrode 30 is colored black, and is smaller than the secondelectrode 40, which is colored white or is highly reflective. When thesmaller, black electrode 30 is placed at a negative voltage potentialrelative to larger, white electrode 40, the positively-charged particles50 migrate to the smaller, black electrode 30. The effect to a viewer ofthe capsule 20 located at position 110 is a mixture of the larger, whiteelectrode 40 and the smaller, black electrode 30, creating an effectwhich is largely white. Referring to FIG. 1B, when the smaller, blackelectrode 30 is placed at a positive voltage potential relative to thelarger, white electrode 40, particles 50 migrate to the larger, whiteelectrode 40 and the viewer is presented a mixture of the blackparticles 50 covering the larger, white electrode 40 and the smaller,black electrode 30, creating an effect which is largely black. In thismanner the capsule 20 may be addressed to display either a white visualstate or a black visual state.

Other two-color schemes are easily provided by varying the color of thesmaller electrode 30 and the particles 50 or by varying the color of thelarger electrode 40. For example, varying the color of the largerelectrode 40 allows fabrication of a rear-addressed, two-color displayhaving black as one of the colors. Alternatively, varying the color ofthe smaller electrode 30 and the particles 50 allow a rear-addressedtwo-color system to be fabricated having white as one of the colors.Further, it is contemplated that the particles 50 and the smallerelectrode 30 can be different colors. In these embodiments, a two-colordisplay may be fabricated having a second color that is different fromthe color of the smaller electrode 30 and the particles 50. For example,a rear-addressed, orange-white display may be fabricated by providingblue particles 50, a red, smaller electrode 30, and a white (or highlyreflective) larger electrode 40. In general, the optical properties ofthe electrodes 30, 40 and the particles 50 can be independently selectedto provide desired display characteristics. In some embodiments theoptical properties of the dispersing fluid 25 may also be varied, e.g.the fluid 25 may be dyed.

In another embodiment, this technique may be used to provide a fullcolor display. Referring now to FIG. 1D, a pixel embodiment is depictedthat comprises three sub-pixels. It should be understood that althoughFIG. 1D depicts a hexagonal pixel having equally-sized sub-pixels, apixel may have any shape and may be comprised of unequal sub-pixels. Thesub-pixels may each be contained in a single large capsule, or each maybe distributed across any number of small microcapsules or microcells.For the purposed of illustration, the simpler case of a single largesub-cell for each sub-pixel is shown. In both cases we refer to theregions, 20, 20′, 20″, as capsules. Thus, a first capsule 20 containspositively charged black particles 50 and a substantially clearsuspending fluid 25. A first, smaller electrode 30 is colored black, andis smaller than the second electrode 40, which is colored red. When thesmaller, black electrode 30 is placed at a negative voltage potentialrelative to larger, red electrode 40, the positively-charged particles50 migrate to the smaller, black electrode 30. The effect to a viewer ofthe capsule 20 located at position 10 is a mixture of the larger, redelectrode 40 and the smaller, black electrode 30, creating an effectwhich is largely red. When the smaller, black electrode 30 is placed ata positive voltage potential relative to the larger, red electrode 40,particles 50 migrate to the larger, red electrode 40 and the viewer ispresented a mixture of the black particles 50 covering the larger, redelectrode 40 and the smaller, black electrode 30, creating an effectwhich is largely black. In this manner the first capsule 20 may beaddressed to display either a red visual state or a black visual state.One can equally have a second capsule 20′ wherein the larger electrode40′ is green, and a third capsule 20″ wherein the larger electrode 40″is blue. A second capsule 20′ contains positively charged blackparticles 50′ and a substantially clear suspending fluid 25′. A first,smaller electrode 30′ is colored black, and is smaller than the secondelectrode 40′, which is colored green. When the smaller, black electrode30′ is placed at a negative voltage potential relative to larger, greenelectrode 40′, the positively-charged particles 50′ migrate to thesmaller, black electrode 30′. The effect to a viewer of the capsule 20′located at position 10′ is a mixture of the larger, green electrode 40′and the smaller, black electrode 30′, creating an effect which islargely green. When the smaller, black electrode 30′ is placed at apositive voltage potential relative to the larger, green electrode 40′,particles 50′ migrate to the larger, green electrode 40′ and the vieweris presented a mixture of the black particles 50′ covering the larger,green electrode 40′ and the smaller, black electrode 30′, creating aneffect which is largely black. Similarly, a third capsule 20″ containspositively charged black particles 50″ and a substantially clearsuspending fluid 25″. A first, smaller electrode 30″ is colored black,and is smaller than the second electrode 40″, which is colored blue.When the smaller, black electrode 30″ is placed at a negative voltagepotential relative to larger, blue electrode 40″, the positively-chargedparticles 50″ migrate to the smaller, black electrode 30″. The effect toa viewer of the capsule 20″ located at position 10″ is a mixture of thelarger, blue electrode 40″ and the smaller, black electrode 30″,creating an effect which is largely blue. When the smaller, blackelectrode 30″ is placed at a positive voltage potential relative to thelarger, blue electrode 40″, particles 50″ migrate to the larger, blueelectrode 40″ and the viewer is presented a mixture of the blackparticles 50″ covering the larger, blue electrode 40″ and the smaller,black electrode 30″, creating an effect which is largely black. Further,the relative intensities of these colors can be controlled by the actualvoltage potentials applied to the electrodes. By choosing appropriatecombinations of the three colors, one may create a visual display whichappears as the effective combination of the selected colors as anadditive process. As an alternative embodiment, the first, second andthird capsules can have larger electrodes 40, 40′, 40″ which arerespectively colored cyan, yellow, and magenta. Operation of thealternative cyan, yellow, and magenta embodiment is analogous to that ofthe red, green, and blue embodiment, with the feature that the color tobe displayed is selected by a subtractive process.

In other embodiments the larger electrode 40 may be reflective insteadof white. In these embodiments, when the particles 50 are moved to thesmaller electrode 30, light reflects off the reflective surface 60associated with the larger electrode 40 and the capsule 20 appears lightin color, e.g. white (see FIG. 2A). When the particles 50 are moved tothe larger electrode 40, the reflecting surface 60 is obscured and thecapsule 20 appears dark (see FIG. 2B) because light is absorbed by theparticles 50 before reaching the reflecting surface 60. The reflectingsurface 60 for the larger electrode 40 may possess retroreflectiveproperties, specular reflection properties, diffuse reflectiveproperties or gain reflection properties. In certain embodiments, thereflective surface 60 reflects light with a Lambertian distribution Thesurface 60 may be provided as a plurality of glass spheres disposed onthe electrode 40, a diffractive reflecting layer such as aholographically formed reflector, a surface patterned to totallyinternally reflect incident light, a brightness-enhancing film, adiffuse reflecting layer, an embossed plastic or metal film, or anyother known reflecting surface. The reflecting surface 60 may beprovided as a separate layer laminated onto the larger electrode 40 orthe reflecting surface 60 may be provided as a unitary part of thelarger electrode 40. In the embodiments depicted by FIGS. 2C and 2D, thereflecting surface may be disposed below the electrodes 30, 40 vis-à-visthe viewpoint 10. In these embodiments, electrode 30 should betransparent so that light may be reflected by surface 60. In otherembodiments, proper switching of the particles may be accomplished witha combination of alternating-current (AC) and direct-current (DC)electric fields and described below in connection with FIGS. 3A–3D.

In still other embodiments, the rear-addressed display previouslydiscussed can be configured to transition between largely transmissiveand largely opaque modes of operation (referred to hereafter as “shuttermode”). Referring back to FIGS. 1A and 1B, in these embodiments thecapsule 20 contains at least one positively-charged particle 50dispersed in a substantially clear dispersing fluid 25. The largerelectrode 40 is transparent and the smaller electrode 30 is opaque. Whenthe smaller, opaque electrode 30 is placed at a negative voltagepotential relative to the larger, transmissive electrode 40, theparticles 50 migrate to the smaller, opaque electrode 30. The effect toa viewer of the capsule 20 located at position 10 is a mixture of thelarger, transparent electrode 40 and the smaller, opaque electrode 30,creating an effect which is largely transparent. Referring to FIG. 1B,when the smaller, opaque electrode 30 is placed at a positive voltagepotential relative to the larger, transparent electrode 40, particles 50migrate to the second electrode 40 and the viewer is presented a mixtureof the opaque particles 50 covering the larger, transparent electrode 40and the smaller, opaque electrode 30, creating an effect which islargely opaque. In this manner, a display formed using the capsulesdepicted in FIGS. 1A and 1B may be switched between transmissive andopaque modes. Such a display can be used to construct a window that canbe rendered opaque. Although FIGS. 1A–2D depict a pair of electrodesassociated with each capsule 20, it should be understood that each pairof electrodes may be associated with more than one capsule 20.

A similar technique may be used in connection with the embodiment ofFIGS. 3A, 3B, 3C, and 3D. Referring to FIG. 3A, a capsule 20 contains atleast one dark or black particle 50 dispersed in a substantially cleardispersing fluid 25. A smaller, opaque electrode 30 and a larger,transparent electrode 40 apply both direct-current (DC) electric fieldsand alternating-current (AC) fields to the capsule 20. A DC field can beapplied to the capsule 20 to cause the particles 50 to migrate towardsthe smaller electrode 30. For example, if the particles 50 arepositively charged, the smaller electrode is placed a voltage that ismore negative than the larger electrode 40. Although FIGS. 3A–3D depictonly one capsule per electrode pair, multiple capsules may be addressedusing the same electrode pair.

The smaller electrode 30 is at most one-half the size of the largerelectrode 40. In preferred embodiments the smaller electrode isone-quarter the size of the larger electrode 40; in more preferredembodiments the smaller electrode 30 is one-eighth the size of thelarger electrode 40. In even more preferred embodiments, the smallerelectrode 30 is one-sixteenth the size of the larger electrode 40.

Causing the particles 50 to migrate to the smaller electrode 30, asdepicted in FIG. 3A, allows incident light to pass through the larger,transparent electrode 40 and be reflected by a reflecting surface 60. Inshutter mode, the reflecting surface 60 is replaced by a translucentlayer, a transparent layer, or a layer is not provided at all, andincident light is allowed to pass through the capsule 20, i.e. thecapsule 20 is transmissive. If the translucent layer or the transparentlayer comprises a color, such as a color filter, the light which istransmitted will be those wavelengths that the filter passes, and thereflected light will consist of those wavelengths that the filterreflects, while the wavelengths that the filter absorbs will be lost.The visual appearance of a shutter mode display may thus depend onwhether the display is in a transmissive or reflective condition, on thecharacteristics of the filter, and on the position of the viewer.

Referring now to FIG. 3B, the particles 50 are dispersed into thecapsule 20 by applying an AC field to the capsule 20 via the electrodes30, 40. The particles 50, dispersed into the capsule 20 by the AC field,block incident light from passing through the capsule 20, causing it toappear dark at the viewpoint 10. The embodiment depicted in FIGS. 3A–3Bmay be used in shutter mode by not providing the reflecting surface 60and instead providing a translucent layer, a transparent layer, a colorfilter layer, or no layer at all. In shutter mode, application of an ACelectric field causes the capsule 20 to appear opaque. The transparencyof a shutter mode display formed by the apparatus depicted in FIGS.3A–3D may be controlled by the number of capsules addressed using DCfields and AC fields. For example, a display in which every othercapsule 20 is addressed using an AC field would appear fifty percenttransmissive.

FIGS. 3C and 3D depict an embodiment of the electrode structuredescribed above in which electrodes 30, 40 are on “top” of the capsule20, that is, the electrodes 30, 40 are between the viewpoint 10 and thecapsule 20. In these embodiments, both electrodes 30, 40 should betransparent. Transparent polymers can be fabricated using conductivepolymers, such as polyaniline, polythiophenes, or indium tin oxide.These materials may be made soluble so that electrodes can be fabricatedusing coating techniques such as spin coating, spray coating, meniscuscoating, printing techniques, forward and reverse roll coating and thelike. In these embodiments, light passes through the electrodes 30, 40and is either absorbed by the particles 50, reflected by retroreflectinglayer 60 (when provided), transmitted throughout the capsule 20 (whenretroreflecting layer 60 is not provided), or partially transmittedand/or reflected if a color filter is present in place ofretroreflecting layer 60.

Referring to FIG. 3E, three sub-pixel capsules 22, 22′ and 22″ eachcontain at least one white particle 50 dispersed in a substantiallyclear dispersing fluid 25. In one embodiment, each sub-pixel capsule 22,22′ and 22″ has a transparent electrode 42, 42′, and 42″ disposed aboveit and a colored filter 60, 60′ and 60″ disposed below it. A commonreflective surface 70 may be shared behind the color filter layer. In analternative embodiment, the display includes an emissive light source70. Smaller, opaque electrodes 30, 30′ and 30″ and Larger, transparentelectrodes 40, 40′ and 40″ may apply direct-current (DC) electric fieldsand alternating-current (AC) fields to the capsules 20, 20′ and 20″. ADC field can be applied to the capsules 20, 20′ and 20″ to cause theparticles 50, 50′ 50″ to migrate towards the smaller electrodes 30, 30′and 30″. For example, if the particles 50, 50′ and 50″ are positivelycharged, the smaller electrodes 30, 30′ and 30″ are placed a voltagethat is more negative than the larger electrodes 40, 40′ and 40″.

The smaller electrode 30 is at most one-half the size of the largerelectrode 40. In preferred embodiments the smaller electrode 30 isone-quarter the size of the larger electrode 40; in more preferredembodiments the smaller electrode 30 is one-eighth the size of thelarger electrode 40. In even more preferred embodiments, the smallerelectrode 30 is one-sixteenth the size of the larger electrode 40.

Causing the particles 50 to migrate to the smaller electrode 30, asdepicted in the first two capsules of FIG. 3E, allows incident light topass through the larger, transparent electrode 40 filter 60 and reflectoff substrate 70. If the first, second and third filters 60, 60′ and 60″are colored cyan, magenta, and yellow respectively, and the particles 50are white, this system can display full color in a standard two-colorfashion.

The filter layer 60 may be a translucent layer, a transparent layer, acolor filter layer, or a layer is not provided at all, and furthersubstrate 70 may be reflective, emissive, translucent or not provided atall. If the layer 60 comprises a color, such as a color filter, thelight which is transmitted will be those wavelengths that the filterpasses, and the reflected light will consist of those wavelengths thatthe filter reflects, while the wavelengths that the filter absorbs willbe lost. The visual appearance of a the display element in 3E may thusdepend on whether the display is in a transmissive or reflectivecondition, on the characteristics of the filter, and on the position ofthe viewer. In an alternative embodiment layer 60 may be provided on topof the capsule adjacent to electrode 42.

Referring now to FIGS. 3F–3K, one embodiment of a tri-color pixel isdescribed. Clear electrode 42 allows light to pass into capsule 22 andto strike either white particles W, red particles R, or a coloredsubstrate 60. The substrate 60 can be a combination of color filter andnon-colored substrate or it can be provided as a unitary coloredsubstrate. Capsule 22 also includes a suspending fluid that can bedye-colored (possibly eliminating the need for a separate color filter60) or substantially clear. Electrodes 45 and 35 are transparent and maybe equally sized or sized in any suitable manner taking into account therelative particles sizes and mobilities of particles W and R. A gapexists between 45 and 35. Assume that particles W are negatively chargedand particles R are positively charged. In FIG. 3F, top electrode 42 isset at a positive voltage potential relative to bottom electrodes 35 and45, moving particles W to the top and particles R to the bottom and thuswhite is displayed. In FIG. 3G by reversing the polarity of theelectrodes, red is displayed. In both FIGS. 3F and 3G the particlesobscure substrate 60. In FIG. 3H electrode 45 is at a negative voltagepotential relative to electrode 35, while electrode 42 is at a voltagepotential between the potentials of 45 and 35, such as zero.Alternatively, electrode 42 switches between the potentials of 45 and 35so that over time the effective voltage of 42 is again between thepotentials of 45 and 35. In this state, the particles R move towardelectrode 45 and the particles W move toward electrode 35 and bothparticles R and W move away from the gap in the center of the capsule22. This reveals substrate 60, permitting a third color such as cyan tobe imaged. In alternate embodiments the color combinations can differ.The specific colors of the filters and particles need not differ. Thissystem, called “dual particle curtain mode,” can image three arbitrarycolors. In a preferred embodiment the colors are as described whereinone color is white and the other two colors are complements. In thismanner, referring again to FIG. 3H, if a small portion of red is visibleit absorbs part of the light reflected from the cyan substrate and thenet result is black, which may be offset by a small portion of visiblewhite. Thus, the pixel in FIG. 3H may appear to be cyan even if some redand white is visible. As mentioned above, the edges of the pixel may bemasked to hide particles R and W when in the mode shown in FIG. 3H.

Referring now to FIG. 3I, a full-color pixel is shown comprising threesub-pixels, each operating in the manner taught by FIGS. 3F–3H whereinthe colored particles are positively charged, and the white particlesare negatively charged. The system may still function with top electrode42 extended as a common top electrode as shown in FIG. 31. For example,to achieve the state shown, electrodes 42, 45, 35, 45′, 35′, 45″, 35″may be set to voltage potentials −30V, 60V, 60V, −60V, +60V, −60V, +60Vrespectively.

Referring now to FIGS. 3J–3K, an electrode scheme is shown whereby acluster of microcapsules may be addressed for an entire sub-pixel in amanner similar to those described above. Clear electrode 42 allows lightto pass into microcapsules 27 and to strike either white particles W,red particles R, or colored substrate 60. As above, colored substrate 60may be a combination of color filter and non-colored substrate 60 orcolored substrate 60 may be provided as a unitary colored substrate.Capsules 27 include a suspending fluid that may be dye-colored (possiblyeliminating the need for a separate color filter 60) or substantiallyclear. Electrodes 45 and 35 are transparent and may be equally sized orsized in any suitable manner taking into account the relative particlesizes and mobilities of particles W and R. A gap exists between 45 and35. Assume that particles W are negatively charged and particles R arepositively charged. The system operates in the manner described in FIGS.3F–3K, although for any given microcapsule 27 there may be multiplegaps. FIG. 3K illustrates an embodiment of a suitable electrode patternin which 45 and 35 are interdigitated.

Referring now to 3L–3M, an alternate embodiment is shown. Again clearelectrode 42 allows light to pass into capsule 22 and to strike whiteparticles W or red particles R. In the embodiment shown in FIG. 3L,capsule 22 includes a suspending fluid 62 that is dyed cyan. Whenelectrodes 45 and 35 are set at appropriate voltages particles, R and Wmove down to electrodes 45 and 35 respectively, where they are obscuredby light-absorbing suspending fluid 62. Alternatively, as shown in FIG.3M, suspending fluid 62 is substantially clear and a third species ofcyan particles C is included in capsules 22. The cyan particles have arelatively neutral charge. When electrodes 45 and 35 are set atappropriate voltages particles R and W move down to electrodes 45 and 35respectively, revealing the cyan particles.

The addressing structure depicted in FIGS. 3A–3M may be used withelectrophoretic display media and encapsulated electrophoretic displaymedia. FIGS. 3A–3M depict embodiments in which electrode 30, 40 arestatically attached to the display media. In certain embodiments, theparticles 50 exhibit bistability, that is, they are substantiallymotionless in the absence of a electric field.

While various of the substrates described above are reflective, ananalogous technique may be employed wherein the substrates emit light,with the particles again acting in a “shutter mode” to reveal or obscurelight. A preferred substrate for this use is an electroluminiscent (EL)backlight. Such a backlight can be reflective when inactive, often witha whitish-green color, yet emit lights in various wavelengths whenactive. By using whitish EL substrates in place of static whitereflective substrates, it is possible to construct a full-colorreflective display that can also switch its mode of operation to displaya range of colors in an emissive state, permitting operation in lowambient light conditions.

FIGS. 4A and 4B depict an embodiment of a rear-addressing electrodestructure that creates a reflective color display in a manner similar tohalftoning or pointillism. The capsule 20 contains white particles 55dispersed in a clear suspending fluid 25. Electrodes 42, 44, 46, 48 arecolored cyan, magenta, yellow, and white respectively. Referring to FIG.4A, when the colored electrodes 42, 44, 46 are placed at a positivepotential relative to the white electrode 48, negatively-chargedparticles 55 migrate to these three electrodes, causing the capsule 20to present to the viewpoint 10 a mix of the white particles 55 and thewhite electrode 48, creating an effect which is largely white. Referringto FIG. 4B, when electrodes 42, 44, 46 are placed at a negativepotential relative to electrode 48, particles 55 migrate to the whiteelectrode 48, and the eye 10 sees a mix of the white particles 55, thecyan electrode 42, the magenta electrode 44, and the yellow electrode46, creating an effect which is largely black or gray. By addressing theelectrodes, any color can be produced that is possible with asubtractive color process. For example, to cause the capsule 20 todisplay a red color to the viewpoint 10, the yellow electrode 46 and themagenta electrode 42 are set to a voltage potential that is morepositive than the voltage potential applied by the cyan electrode 42 andthe white electrode 48. Further, the relative intensities of thesecolors can be controlled by the actual voltage potentials applied to theelectrodes. Again, AC current may be used appropriately to randomize theposition of the particles as a step in this process.

The technique used in FIGS. 4A and 4B could be used in a similar mannerwith fewer electrodes and controlling fewer colors. For example, ifelectrode 42 were not present, the pixel could still display threecolors. If electrodes 44 and 46 were colored red and cyan respectively,the capsule could display red, cyan and white. This construction couldbe used then employed as a sub-pixel, to be matched with similarsub-pixels displaying other trios of colors thus achieving a full-colordisplay as described above.

In another embodiment, depicted in FIG. 5, a color display is providedby a capsule 20 of size d containing multiple species of particles in aclear, dispersing fluid 25. Each species of particles has differentoptical properties and possess different electrophoretic mobilities (μ)from the other species. In the embodiment depicted in FIG. 5, thecapsule 20 contains red particles 52, blue particles 54, and greenparticles 56, and|μ_(R)|>|μ_(B)|>|μ_(G)|That is, the magnitude of the electrophoretic mobility of the redparticles 52, on average, exceeds the electrophoretic mobility of theblue particles 54, on average, and the electrophoretic mobility of theblue particles 54, on average, exceeds the average electrophoreticmobility of the green particles 56. As an example, there may be aspecies of red particle with a zeta potential of 100 millivolts (mV), ablue particle with a zeta potential of 60 mV, and a green particle witha zeta potential of 20 mV. The capsule 20 is placed between twoelectrodes 32, 42 that apply an electric field to the capsule. Byaddressing the capsule 20 with positive and negative voltage fields ofvarying time durations, it is possible to move any of the variousparticle species to the top of the capsule to present a certain color.

FIGS. 6A–6B depict the steps to be taken to address the display shown inFIG. 5 to display a red color to a viewpoint 10. Referring to FIG. 6A,all the particles 52, 54, 56 are attracted to one side of the capsule 20by applying an electric field in one direction. The electric fieldshould be applied to the capsule 20 long enough to attract even the moreslowly moving green particles 56 to the electrode 34. Referring to FIG.6B, the electric field is reversed just long enough to allow the redparticles 52 to migrate towards the electrode 32. The blue particles 54and green particles 56 will also move in the reversed electric field,but they will not move as fast as the red particles 52 and thus will beobscured by the red particles 52. The amount of time for which theapplied electric field must be reversed can be determined from therelative electrophoretic mobilities of the particles, the strength ofthe applied electric field, and the size of the capsule.

FIGS. 7A–7D depict addressing the display element to a blue state. Asshown in FIG. 7A, the particles 52, 54, 56 are initially randomlydispersed in the capsule 20. All the particles 52, 54, 56 are attractedto one side of the capsule 20 by applying an electric field in onedirection (shown in FIG. 7B). Referring to FIG. 7C, the electric fieldis reversed just long enough to allow the red particles 52 and blueparticles 54 to migrate towards the electrode 32. The amount of time forwhich the applied electric field must be reversed can be determined fromthe relative electrophoretic mobilities of the particles, the strengthof the applied electric field, and the size of the capsule. Referring toFIG. 7D, the electric field is then reversed a second time and the redparticles 52, moving faster than the blue particles 54, leave the blueparticles 54 exposed to the viewpoint 10. The amount of time for whichthe applied electric field must be reversed can be determined from therelative electrophoretic mobilities of the particles, the strength ofthe applied electric field, and the size of the capsule.

FIGS. 8A–8C depict the steps to be taken to present a green display tothe viewpoint 10. As shown in FIG. 8A, the particles 52, 54, 56 areinitially distributed randomly in the capsule 20. All the particles 52,54, 56 are attracted to the side of the capsule 20 proximal theviewpoint 10 by applying an electric field in one direction. Theelectric field should be applied to the capsule 20 long enough toattract even the more slowly moving green particles 56 to the electrode32. As shown in FIG. 8C, the electric field is reversed just long enoughto allow the red particles 52 and the blue particles 54 to migratetowards the electrode 54, leaving the slowly-moving green particles 56displayed to the viewpoint. The amount of time for which the appliedelectric field must be reversed can be determined from the relativeelectrophoretic mobilities of the particles, the strength of the appliedelectric field, and the size of the capsule.

In other embodiments, the capsule contains multiple species of particlesand a dyed dispersing fluid that acts as one of the colors. In stillother embodiments, more than three species of particles may be providedhaving additional colors. In one of these embodiments, the capsulecontains white particles which have a strong positive charge, cyanparticles which have a weakly positive charge, and red particles havinga negative charge. Since the electrophoretic mobilities of these typesof particles will be proportional to charge and of a direction relatedto the sign or polarity of the charge, these three types of particleswill have different mobilities in the same voltage field. In thisexample, white is achieved when the top electrode is negative and thebottom electrode is positive. Red is achieved when the top electrode ispositive and the bottom electrode is negative. Cyan is achieved by firstsetting the sub-pixel to white and then briefly reversing the voltagefield so that the higher mobility white particles migrate past the cyanparticles and the lower mobility, or slower, cyan particles remaintopmost and visible. Although FIGS. 6–8C depict two electrodesassociated with a single capsule, the electrodes may address multiplecapsules or less than a full capsule.

The addressing structures described in FIGS. 1–8 typically comprise atop electrode controlled by display driver circuitry. It may be seenthat if the top electrode is absent, the display may be imaged by anexternally applied voltage source, such as a passing stylus orelectrostatic print head. The means that techniques applied above togenerate a full-color electrophoretic display could also be applied fora full-color electrophoretic media.

In FIG. 9, the rear electrode structure can be made entirely of printedlayers. A conductive layer 166 can be printed onto the back of a displaycomprised of a clear, front electrode 168 and a printable displaymaterial 170. A clear electrode may be fabricated from indium tin oxideor conductive polymers such as polyanilines and polythiophenes. Adielectric coating 176 can be printed leaving areas for vias. Then, theback layer of conductive ink 178 can be printed. If necessary, anadditional layer of conductive ink can be used before the final inkstructure is printed to fill in the holes.

This technique for printing displays can be used to build the rearelectrode structure on a display or to construct two separate layersthat are laminated together to form the display. For example anelectronically active ink may be printed on an indium tin oxideelectrode. Separately, a rear electrode structure as described above canbe printed on a suitable substrate, such as plastic, polymer films, orglass. The electrode structure and the display element can be laminatedto form a display.

Referring now to FIG. 10, a threshold may be introduced into anelectrophoretic display cell by the introduction of a third electrode.One side of the cell is a continuous, transparent electrode 200 (anode).On the other side of the cell, the transparent electrode is patternedinto a set of isolated column electrode strips 210. An insulator 212covers the column electrodes 210, and an electrode layer on top of theinsulator is divided into a set of isolated row electrode strips 230,which are oriented orthogonal to the column electrodes 210. The rowelectrodes 230 are patterned into a dense array of holes, or a grid,beneath which the exposed insulator 212 has been removed, forming amultiplicity of physical and potential wells.

A positively charged particle 50 is loaded into the potential wells byapplying a positive potential (e.g. 30V) to all the column electrodes210 while keeping the row electrodes 230 at a less positive potential(e.g. 15V) and the anode 200 at zero volts. The particle 50 may be aconformable capsule that situates itself into the physical wells of thecontrol grid. The control grid itself may have a rectangularcross-section, or the grid structure may be triangular in profile. Itcan also be a different shape which encourages the microcapsules tosituate in the grid, for example, hemispherical.

The anode 200 is then reset to a positive potential (e.g. 50V). Theparticle will remain in the potential wells due to the potentialdifference in the potential wells: this is called the Hold condition. Toaddress a display element the potential on the column electrodeassociated with that element is reduced, e.g. by a factor of two, andthe potential on the row electrode associated with that element is madeequal to or greater than the potential on the column electrode. Theparticles in this element will then be transported by the electric fielddue to the positive voltage on the anode 200. The potential differencebetween row and column electrodes for the remaining display elements isnow less than half of that in the normal Hold condition. The geometry ofthe potential well structure and voltage levels are chosen such thatthis also constitutes a Hold condition, i.e., no particles will leavethese other display elements and hence there will be no half-selectproblems. This addressing method can select and write any desiredelement in a matrix without affecting the pigment in any other displayelement. A control electrode device can be operated such that the anodeelectrode side of the cell is viewed.

The control grid may be manufactured through any of the processes knownin the art, or by several novel processes described herein. That is,according to traditional practices, the control grid may be constructedwith one or more steps of photolithography and subsequent etching, orthe control grid may be fabricated with a mask and a “sandblasting”technique.

In another embodiment, the control grid is fabricated by an embossingtechnique on a plastic substrate. The grid electrodes may be depositedby vacuum deposition or sputtering, either before or after the embossingstep. In another embodiment, the electrodes are printed onto the gridstructure after it is formed, the electrodes consisting of some kind ofprintable conductive material which need not be clear (e.g. a metal orcarbon-doped polymer, an intrinsically conducting polymer, etc.).

In a preferred embodiment, the control grid is fabricated with a seriesof printing steps. The grid structure is built up in a series of one ormore printed layers after the cathode has been deposited, and the gridelectrode is printed onto the grid structure. There may be additionalinsulator on top of the grid electrode, and there may be multiple gridelectrodes separated by insulator in the grid structure. The gridelectrode may not occupy the entire width of the grid structure, and mayonly occupy a central region of the structure, in order to stay withinreproducible tolerances. In another embodiment, the control grid isfabricated by photoetching away a glass, such as a photostructuralglass.

In an encapsulated electrophoretic image display, an electrophoreticsuspension, such as the ones described previously, is placed insidediscrete compartments that are dispersed in a polymer matrix. Thisresulting material is highly susceptible to an electric field across thethickness of the film. Such a field is normally applied using electrodesattached to either side of the material. However, as described above inconnection with FIGS. 3A–3F, some display media may be addressed bywriting electrostatic charge onto one side of the display material. Theother side normally has a clear or opaque electrode. For example, asheet of encapsulated electrophoretic display media can be addressedwith a head providing DC voltages.

In another embodiment, the encapsulated electrophoretic suspension canbe printed onto an area of a conductive material such as a printedsilver or graphite ink, aluminized mylar, or any other conductivesurface. This surface which constitutes one electrode of the display canbe set at ground or high voltage. An electrostatic head consisting ofmany electrodes can be passed over the capsules to addressing them.Alternatively, a stylus can be used to address the encapsulatedelectrophoretic suspension.

In another embodiment, an electrostatic write head is passed over thesurface of the material. This allows very high resolution addressing.Since encapsulated electrophoretic material can be placed on plastic, itis flexible. This allows the material to be passed through normal paperhandling equipment. Such a system works much like a photocopier, butwith no consumables. The sheet of display material passes through themachine and an electrostatic or electrophotographic head addresses thesheet of material.

In another embodiment, electrical charge is built up on the surface ofthe encapsulated display material or on a dielectric sheet throughfrictional or triboelectric charging. The charge can built up using anelectrode that is later removed. In another embodiment, charge is builtup on the surface of the encapsulated display by using a sheet ofpiezoelectric material.

Microencapsulated displays offer a useful means of creating electronicdisplays, many of which can be coated or printed. There are manyversions of microencapsulated displays, including microencapsulatedelectrophoretic displays. These displays can be made to be highlyreflective, bistable, and low power.

To obtain high resolution displays, it is useful to use some externaladdressing means with the microencapsulated material. This inventiondescribes useful combinations of addressing means with microencapsulatedelectrophoretic materials in order to obtain high resolution displays.

One method of addressing liquid crystal displays is the use ofsilicon-based thin film transistors to form an addressing backplane forthe liquid crystal. For liquid crystal displays, these thin filmtransistors are typically deposited on glass, and are typically madefrom amorphous silicon or polysilicon. Other electronic circuits (suchas drive electronics or logic) are sometimes integrated into theperiphery of the display. An emerging field is the deposition ofamorphous or polysilicon devices onto flexible substrates such as metalfoils or plastic films.

The addressing electronic backplane could incorporate diodes as thenonlinear element, rather than transistors. Diode-based active matrixarrays have been demonstrated as being compatible with liquid crystaldisplays to form high resolution devices.

There are also examples of crystalline silicon transistors being used onglass substrates. Crystalline silicon possesses very high mobilities,and thus can be used to make high performance devices. Presently, themost straightforward way of constructing crystalline silicon devices ison a silicon wafer. For use in many types of liquid crystal displays,the crystalline silicon circuit is constructed on a silicon wafer, andthen transferred to a glass substrate by a “liftoff” process.Alternatively, the silicon transistors can be formed on a silicon wafer,removed via a liftoff process, and then deposited on a flexiblesubstrate such as plastic, metal foil, or paper. As another embodiment,the silicon could be formed on a different substrate that is able totolerate high temperatures (such as glass or metal foils), lifted off,and transferred to a flexible substrate. As yet another embodiment, thesilicon transistors are formed on a silicon wafer, which is then used inwhole or in part as one of the substrates for the display.

The use of silicon-based circuits with liquid crystals is the basis of alarge industry. Nevertheless, these display possess serious drawbacks.Liquid crystal displays are inefficient with light, so that most liquidcrystal displays require some sort of backlighting. Reflective liquidcrystal displays can be constructed, but are typically very dim, due tothe presence of polarizers. Most liquid crystal devices require precisespacing of the cell gap, so that they are not very compatible withflexible substrates. Most liquid crystal displays require a “rubbing”process to align the liquid crystals, which is both difficult to controland has the potential for damaging the TFT array.

The combination of these thin film transistors with microencapsulatedelectrophoretic displays should be even more advantageous than withliquid crystal displays. Thin film transistor arrays similar to thoseused with liquid crystals could also be used with the microencapsulateddisplay medium. As noted above, liquid crystal arrays typically requiresa “rubbing” process to align the liquid crystals, which can cause eithermechanical or static electrical damage to the transistor array. No suchrubbing is needed for microencapsulated displays, improving yields andsimplifying the construction process.

Microencapsulated electrophoretic displays can be highly reflective.This provides an advantage in high-resolution displays, as a backlightis not required for good visibility. Also, a high-resolution display canbe built on opaque substrates, which opens up a range of new materialsfor the deposition of thin film transistor arrays.

Moreover, the encapsulated electrophoretic display is highly compatiblewith flexible substrates. This enables high-resolution TFT displays inwhich the transistors are deposited on flexible substrates like flexibleglass, plastics, or metal foils. The flexible substrate used with anytype of thin film transistor or other nonlinear element need not be asingle sheet of glass, plastic, metal foil, though. Instead, it could beconstructed of paper. Alternatively, it could be constructed of a wovenmaterial. Alternatively, it could be a composite or layered combinationof these materials.

As in liquid crystal displays, external logic or drive circuitry can bebuilt on the same substrate as the thin film transistor switches.

In another embodiment, the addressing electronic backplane couldincorporate diodes as the nonlinear element, rather than transistors.

In another embodiment, it is possible to form transistors on a siliconwafer, dice the transistors, and place them in a large area array toform a large, TFT-addressed display medium. One example of this conceptis to form mechanical impressions in the receiving substrate, and thencover the substrate with a slurry or other form of the transistors. Withagitation, the transistors will fall into the impressions, where theycan be bonded and incorporated into the device circuitry. The receivingsubstrate could be glass, plastic, or other nonconductive material. Inthis way, the economy of creating transistors using standard processingmethods can be used to create large-area displays without the need forlarge area silicon processing equipment.

While the examples described here are listed using encapsulatedelectrophoretic displays, there are other particle-based display mediawhich should also work as well, including encapsulated suspendedparticles and rotating ball displays.

While the invention has been particularly shown and described withreference to specific preferred embodiments, it should be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

1. A full-color electrophoretic display element comprising: a firstcapsule comprising a plurality of white particles and a plurality of redparticles; a second capsule comprising a plurality of white particlesand a plurality of green particles; and a third capsule comprising aplurality of white particles and a plurality of blue particles; whereinthe element presents a visual display in response to the application ofan electrical signal to at least one of the first capsule, the secondcapsule, and the third capsule; and wherein a white visual display isprovided by at least the plurality of white particles in at least one ofthe first; second, and third capsules.
 2. The display element of claim 1wherein the capsule further includes a suspending fluid.
 3. The displayelement of claim 2 wherein the suspending fluid is substantially clear.4. The display element of claim 2 wherein the suspending fluid is dyed.5. The display element of claim 1 further comprising a plurality ofelectrodes, wherein at least one of the first, second, and thirdcapsules is addressed by a plurality of electrodes.
 6. The displayapparatus of claim 5 wherein at least one of the plurality of electrodeshas a size different from another of the plurality of electrodes.
 7. Thedisplay apparatus of claim 5 wherein at least one of the plurality ofelectrodes has a color different from another of the plurality ofelectrodes.
 8. A full-color electrophoretic display element comprising:a first capsule comprising a plurality of white particles and aplurality of cyan particles; a second capsule comprising a plurality ofwhite particles and a plurality of magenta particles; and a thirdcapsule comprising a plurality of white particles and a plurality ofyellow particles; wherein the element presents a visual display inresponse to the application of an electrical signal to at least one ofthe first capsule, the second capsule, and the third capsule; andwherein a white visual display is provided by at least the plurality ofwhite particles in at least one of the first, second, and thirdcapsules.
 9. The display element of claim 8 wherein the capsule furtherincludes a suspending fluid.
 10. The display element of claim 9 whereinthe suspending fluid is substantially clear.
 11. The display element ofclaim 9 wherein the suspending fluid is dyed.
 12. The display element ofclaim 8 further comprising a plurality of electrodes, wherein at leastone of the first, second, and third capsules is addressed by a pluralityof electrodes.
 13. The display apparatus of claim 12 wherein at leastone of the plurality of electrodes has a size different from another ofthe plurality of electrodes.
 14. The display apparatus of claim 12wherein at least one of the plurality of electrodes has a colordifferent from another of the plurality of electrodes.